In order to improve properties of various base materials, attempts have heretofore been made to vacuum-evaporate a film on the surfaces thereof by a plasma CVD method. In the field of packing materials, it is a known practice to vacuum-evaporate a film on a plastic base material such as of a container by the plasma CVD method in order to improve gas shut-off property. For example, it has been attempted to improve gas-barrier properties by vacuum-evaporating silicon oxide film on the surface of a plastic container such as a polyethylene terephthalate (PET) bottle by the plasma CVD method.
In recent years, a polylactic acid which is a representative biodegradable plastic material is drawing attention in various fields from the standpoint of environmental problems. In the field of packing materials, too, bottles made from the polylactic acid have been put into practical use. The polylactic acid bottles are inferior in gas-barrier property to the PET bottles. Therefore, attempts have been made to vacuum-evaporate the film on the polylactic acid bottles, too, in order to improve gas-barrier property and the like properties.
Silicon oxide exhibits excellent gas-barrier property when it is vacuum-evaporated onto the PET bottles but invites various problems when it is vacuum-evaporated onto containers made from a resin having a low glass transition point and a low heat resistance, such as the polylactic acid. That is, the polylactic acid has a glass transition point (Tg) of 58° C. and is thermally inferior to PET (e.g., PET has a Tg of 70° C.). That is, in order to exhibit barrier property, the silicon oxide must be vacuum-evaporated under a high-output condition (usually, vacuum evaporation with a microwave output of not less than 600 W for not shorter than 4 sec) while using an oxygen gas and an organometal gas. When vacuum-evaporated under such a high-output condition, the wall of polylactic acid bottle is thermally deformed and thermally deteriorated due to the heat of oxygen plasma and other plasma occurring in the step of vacuum evaporation, and offensive odor generates in the bottle. Further, the vacuum-evaporated film of silicon oxide is hard, brittle and lacks flexibility, and forms a hydrophilic group such as silanol group. Therefore, the vacuum-evaporated film of silicon oxide poorly follows deformation of the polylactic acid base material, not so closely adheres thereto and, besides, exhibits low barrier property against water.
Under such circumstances, vacuum-evaporated films of other than the silicon oxide have been extensively studied. For example, patent documents 1 and 2 are proposing vacuum-evaporating a hydrocarbon film called diamond-like carbon film (DLC film) on the inner surfaces of the polylactic acid bottles. Further, a patent document 3 is proposing forming, on the surface of a plastic container, a DLC film (long-chain branched type) comprising amorphous carbon as a chief component, the compositions of CH3, CH2 and CH in the film being at a ratio of 25%, 60% and 15% based on the sum of these three components.    Patent document 1: JP-A-2001-18290    Patent document 2: JP-A-2005-14966    Patent document 3: JP-A-2006-131306